Hillary Clinton attached that line as a hashtag to a tweet about the importance of measles vaccinations earlier this month. Given that Mrs Clinton's tweets are read like messages from the Delphic oracle, it has rekindled speculation that the former secretary of state will be leaning on her new grandmatronly status in her all-but-announced upcoming presidential campaign.

Since Chelsea Clinton gave birth to her daughter, Charlotte, last September, Hillary Clinton has frequently mentioned how being a grandmother has given her a renewed interest in ensuring the security of future generations - which, come to think of it, sounds like a pretty reliable campaign theme.

Perhaps more importantly for Mrs Clinton, however, it's also a humanising theme.

"I think it's a way to soften her image and make her seem very relatable," explains Jennifer Lawless, director of American University's Women & Politics Institute.

Lawless says that US voters want two sets of traits in their leaders - competency and empathy. In 2008 then-Senator Clinton demonstrated that she was competent, but she often came across as cold and mechanical.

One of the few times Mrs Clinton showed a more personal side was when she choked up while talking about why she was running for president - and it resulted in an overnight boost in her fortunes.

"Some people think elections are a game, lot's of who's up or who's down," she said. "It's about our country, it's about our kids' futures, and it's really about all of us together."

The following day she upset Barack Obama in the New Hampshire primary, giving her the momentum to wage a long, although ultimately losing, battle for the Democratic nomination.

Mrs Clinton has yet to formally enter the 2016 race - and she appears to be in no rush to do so, since a credible opponent for the Democratic presidential nomination has yet to emerge. Given the tight-lipped nature of Mrs Clinton's operation up to this point, political analysts have been poring over even the smallest signs that could indicate how she will run this time around - and what lessons, if any, she has learned from her 2008 defeat.

The grandmother-knows-best tweet, then, has been heralded as something of a revelation.

According to the Atlantic's Peter Beinart, Mrs Clinton as "grandmother-in-chief" not only softens her occasionally hard edges, it fits nicely with her political worldview.

"In the popular imagination, grandmothers are both caring and conservative," he writes. "They dote on their grandchildren while also tut-tutting about a culture gone awry. They are pro-family in both the liberal and conservative senses of the word."

Mrs Clinton has always said she's both a "trailblazer and a traditionalist", Beinart says. "Now, by running as a grandmother, she may finally make Americans believe her."

The tactic is not without its risks, however. Mrs Clinton's political opponents have been quick to point out that she will be 69 on election day in 2016, the same age as the nation's oldest president, Ronald Reagan, when he was first elected in 1980.

Some commentators, including Republican strategist Karl Rove, have gone so far as to question Mrs Clinton's health and fitness for the rigours of office.

Could a campaign that touts the wisdom of a grandmother play into these lines of attack?

"The image of a blue-haired granny is a tried-and-true American stereotype, and one that is antithetical to the image of the commander-in-chief with his finger on the button," writes Time magazine's Jay Newton-Small.

According to Lawless, however, Mrs Clinton's age was going to be a factor one way or the other, so she might as well tackle the issue head-on and turn a possible weakness into a strength.

"Better to be thought of as an old and empathetic person than just old," she says.

Others on the right simply condemned Mrs Clinton's tweet as a calculated move from an always-calculating political family.

"Clinton's flaunting of her grandchild is one of the most transparently cynical and sentimental acts of a major American politician that I can recall," Matthew Continetti of the Washington Free Beacon writes. "We have had presidents who have been parents, and we have had presidents who have been grandparents. But a campaign based on grandparental solidarity? A novelty."

The line quickly gave rise to the quip that a Clinton presidency will advance the "granny state" - a haggard iteration of the liberal nanny state.

"#GrandmothersKnowBest feels like a hashtag the GOP would have come up with for Hillary," tweets Jon Passantino, Buzzfeed's deputy news director.

Although Mrs Clinton is treading new ground as the first woman with a realistic shot at the US presidency, it's familiar territory for other female world leaders - who have addressed the issue with varying levels of directness.

One of German Chancellor Angela Merkel's public nicknames is "Mutti" - Mummy - but she largely has kept her personal life under tight wraps. In the most recent campaign, however, she did make appearances with her husband's grandchildren.

On the other end of the spectrum is Liberian President Ellen Johnson Sirleaf. The 76-year-old grandmother of eight campaigned on the slogan that she wanted to bring "motherly sensitivity and emotion" to the office.

Image copyrightGetty ImagesImage caption
Mitt Romney often appeared with his grandchildren at 2012 campaign events

The humanising effect of having youngsters in tow during a campaign appearance isn't limited to female candidates, of course. In 2012 Republican presidential nominee Mitt Romney often brought some of his 18 grandchildren onto the public stage, and photographs of his entire brood were used in television adverts.

Liberia isn't the US, however, and while Mr Romney assuredly needed a humanising touch as well, the downside of playing up his role as pater familias was minimal compared to the challenges facing Mrs Clinton.

Still, says Lawless, the benefits of the strategy likely outweigh the risks. And if a single hashtag means Mrs Clinton will be placing new emphasis on the groundbreaking nature of her candidacy - which recent polls show could help broaden her appeal - the potential benefit is all the greater.

"Her line about putting 18 million cracks in the glass ceiling was one of the most successful," Lawless says. Although Mrs Clinton didn't use it until she was conceding defeat to Mr Obama, this time could be different.

"Grandmothers know best" may have been just one hashtag on one tweet, but there is almost certainly more to it than that.